Cellulose ethers are commonly employed commercially to form capsules which are adapted to contain and orally deliver pharmaceutical agents and medicaments. Preferred cellulose ethers for such applications are methylcellulose and hydroxypropylmethylcellulose.
Cellulose ether capsules are typically manufactured by dipping hot pins in a cold, aqueous cellulose ether dip coating solution. The solution gels on the pins and water evaporates during a drying step to form thin film layers of dried cellulose ether around the hot pins. The thin films take the form of caps and bodies, which are then removed from the pins. Caps are mated with bodies to form capsules. Analogous processes exist wherein cold pins are dipped in a hot, aqueous cellulose ether solution. Processes for making capsules are seen in U.S. Pat. Nos. 3,617,588;4,001,211;4,917,885; and 5,756,036, which are incorporated herein by reference.
A problem commonly encountered in manufacturing cellulose ether capsules is haze formation at their inner surfaces. Haze formation is most noticeable in transparent capsules.
Haze causes cellulose ether capsules to exhibit less luster and gloss than they would otherwise. Due to haze, cellulose ether capsules typically do not have the same level of luster as gelatin capsules. This difference in appearance is discussed in "HPMC Capsules--An Alternative to Gelatin," Pharmaceutical Technology Europe 10(11) (1998).
It would be desirable to have cellulose ether capsules which are substantially free of haze formation at their interior surfaces and a process for making such capsules. It would also be desirable to have a process for making a cellulose ether composition useful in such capsules.